1. Field of the Invention
This invention relates to a data communication apparatus, and, in particular, to a high-speed facsimile machine capable of carrying out a plurality of functions at the same time thereby allowing to shorten the data processing time period. More in particular, the present invention relates to a facsimile machine of the band compression type in which communication of data is carried out in the form of codes. Still more specifically, the present invention is concerned with a facsimile communication machine provided with a system control unit including a pair of one-chip micro-CPUs, wherein it is so structured that one of the CPUs is capable of controlling the reading operation while the machine is in transmission mode and of controlling the recording operation while the machine is in receiving mode and the other CPU is capable of controlling the coding operation while the machine is in transmission mode and of controlling the decoding operation while the machine is in receiving mode, thereby allowing to increase the data processing speed.
2. Description of the Prior Art
In general, in a facsimile machine which carries out communication with the use of coded data, various control functions are required such as I/O device control, sequence control, protocol control, data compressing and restoring control in a MH or MR coding system, operating port control, scanner unit control, MODEM control, recording head driver control and power supply sequence control. These control functions are usually carried out under the supervision of a system control unit provided in the facsimile machine.
When such a system control unit is structured to have a single micro-CPU, there is a limit in data processing speed. However, as well known in the art, by constructing a part of such a system control unit in the form of so-called firmware, for example for that portion of the unit which carries out the steps, after reading picture information by a scanner, of run-length counting, coding and generation of data transmission format, or for that portion of the unit which carries out the steps, after transfer of received picture data to a micro-CPU through a bus, of decoding the received picture data, conversion to picture information and transfer of data to a recording device, there may be provided a facsimile machine including a single micro-CPU, which has the ability of MODEM rate 4,800 bps and 20 ms/line of I/O speed in the MH coding system.
Furthermore, also well known is a facsimile control method wherein, in order to increase the data processing speed, use is made of two micro-CPUs thereby allowing to carry out picture signal control in the form of parallel processing format with assigning communication and terminal controls or transmitting and receiving controls to respective CPUs. According to such a facsimile control method, it is true that the data processing speed may be increased by the factor of 1 to 2 as compared with the above-described approach depending on the nature of an original to be transmitted. However, such a method cannot guarantee an increase in processing speed of twice or more.
Thus, there has been a need to further increase the data processing speed of a facsimile machine.